2025 SWPO striped marlin stock assessment modelling workshop

January 2025

Overview

  • SPC presented the 2024 SWPO striped marlin stock assessment to SC20 and identified issues with fits to the index and size composition data.
  • SC20 requested these issues be addressed and presented to SC21
  • The US offered to assist in the redevelopment of the stock assessment and host SPC staff for a modelling workshop.

Developments since SC20

Improving the fit to the size composition data

  • Multifan-CL can only implement selectivity at age, and spline selectivity nodes can only be on age points
  • Improving the resolution of the selectivity curve was accomplished by moving to a quarterly population dynamics model
  • Unfortunately this results in seasonal recruitment dynamics which are inconsistent with our understanding of striped marlin biology

Transition to Stock Synthesis


  • Stock Synthesis can model selectivity at length
  • Improves the resolution of the selectivity curve and fit to the composition data while maintaining annual population dynamics

Remaining issues

Data

  • Conflict between AU length/weight data
  • Non-representative composition data (mixed flag fisheries)
  • Representativeness of the CPUE index (large spike)
  • Inclusion of TW size composition data

Model structure

  • Model start year (1952 v. 1979)
  • Data-weighting
  • Refine growth parameterization (estimate internally using CAAL)
  • Refine selectivities (time-blocks or seasonal selectivity)
  • 2 sex model
  • Dealing with large catch in 1954

Workshop workplan


  • Acknowledging that it may be difficult to progress on data issues at this stage, progress on identified issues where possible
  • Help prioritize a workplan for SPC to undertake prior to PAW
  • Identify how the US can continue to provide support
  • Begin documenting workshop activities

Running models

Please conduct model developments in your own branch of the repository

git checkout -b <branch-name>

Use 00-test-stock-synthesis-workflow.r as a template for script based model development.